(a) The Field of the Invention
This invention refers to an oven for firing ceramic materials, which oven has a high thermal efficiency and has other original and advantageous structural and operational characteristics which will appear from the description thereof.
The ceramic materials in question are mainly tiles for flooring, wall coverings, and the like, but the invention is not limited thereto and is applicable to ceramic materials different from tiles, provided that they may be processed in the apparatus according to the invention.
(B) The Prior Art
It is known to fire ceramic materials, in particular tiles, by various processes and various types of apparatus. Not considering all the operations and devices which are not connected with the firing stage to which the invention refers, and thus not considering the mechanical formation of the tile bodies, the application of the glaze thereto, their drying, their transport or storage, the loading and unloading operations, etc., it may be recalled that the firing of tiles is carried out mainly according to the two stage or to the single stage processes. In the first case the ceramic tile body is fired firstly without the glaze coating, whereby the so-called "bisque" is produced, and subsequently the bisque is covered with glaze and the glaze is fired and vitrified in turn. In the single stage firing process, on the contrary, the raw tile body is coated with liquid glaze and the whole is fired in one operation. The invention herein to be described is independent of the particular process employed, inasmuch as it is applicable both to the firing of ceramic bodies and to the firing of the glaze on the bisque, as well as to the single stage firing of raw ceramic bodies already coated with glaze.
Further, the invention is independent from the particular compositions both of the ceramic body and of the glaze, and is therefore independent from the particular thermal diagram which it is desired to follow in the firing, in each specific case. As is known, it is customary to introduce into the firing ovens the raw tile or tile body or the bisque with the raw glaze (and since there is no need, as far as this invention is concerned, to distinguish between these various cases, the word "tile" will always be used to refer miscellaneously to all of them) in a dried condition and therefore at a temperature above room temperature but not very high, as e.g. about 100.degree.-300.degree. C., and to heat it in a first section of the firing oven, with a heating rate which depends on many factors, both chemical and mechanical, and which varies from case to case, until it has been brought to temperatures which are very close to the maximum firing temperatures. Thereafter the heating proceeds generally more slowly, the temperature curve flattens out at a certain point--and may even show a maximum, though not a sharp one, and then slope down slightly--all this in a firing zone appear. A lowering of the temperature, optionally a fairly sharp one, follows before the tiles leave the oven, due to a direct or indirect cooling to which it is convenient to subject the tiles in the end zone.
A first distinction between various known processes and corresponding apparatus, consists in the different mechanical means used for advancing the tiles along the oven. In some apparatus-- more properly called "tunnel ovens"--the tiles are loaded onto trucks or other supports, each of which carries a plurality of tiles, and then the trucks or supports are caused by any suitable means to travel through the oven at the desired speed. In other types of ovens, the tiles are advanced, it may be said, individually, i.e. are individually deposited onto conveyors and in theory should all move along the oven at the same speed, and therefore maintain without change the mutual position resulting from their loading. In case of failures which may always occur, such as tile breakage, blocks, and the like, means must be provided, and are provided in different ways in the various apparatus, for re-establishing the regular flow of the tiles.